Introduction

The 74LS74 is a dual D-type flip-flop with Set (S) and Reset (R) pins. It can store 1-bit of data, and is widely used in memory elements, shift registers, and data synchronization circuits. In this experiment, we will explore how the D flip-flop can be used to store data based on a clock signal.

Materials Required

• 74LS74 D Flip-Flop IC
• Switches for D input, clock, Set, and Reset
• LEDs to observe the outputs (Q and Q')
• Breadboard and connecting wires
• Power supply (5V)

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Circuit Diagram

Below is the circuit diagram for the 74LS74 D Flip-Flop experiment:

Pin Configuration

The 74LS74 IC has 14 pins. Below is the pin configuration:

• D: Data input
• Q: Output
• Q’: Complement output
• CLK: Clock input (rising-edge triggered)
• S: Set input (active high)
• R: Reset input (active high)
• VCC: +5V power supply
• GND: Ground

Steps for the Experiment

1. Place the 74LS74 IC on the breadboard.
2. Connect a switch to the D input pin (data input).
3. Connect another switch to the CLK pin (clock input) to trigger data storage.
4. Connect two LEDs to the output pins Q and Q' to observe the stored data and its complement.
5. Use switches for Set and Reset inputs to directly control the flip-flop state if needed.
6. Connect the power supply (5V) to the VCC and GND pins of the IC.
7. Toggle the D input and press the clock button to store the data in the flip-flop, which will then reflect on the Q and Q’ outputs.

Explanation

The 74LS74 D flip-flop stores data based on the state of the D input when a rising edge of the clock signal occurs. The Q output takes on the value of the D input, while Q' is the complement of Q. The Set (S) and Reset (R) inputs provide additional control:

• If Set (S) is activated (high), the Q output goes high, and Q’ goes low regardless of the clock or D input.
• If Reset (R) is activated (high), the Q output goes low, and Q’ goes high.
• During normal operation, data from D is stored on the rising edge of the clock signal.

Results and Observations

When the clock signal goes from low to high (rising edge), the value of the D input is stored in the flip-flop, and the Q output reflects this value. The Q' output will always be the complement of Q. The Set and Reset inputs override normal clock operation when activated.

• When the D input is HIGH and the clock pulse occurs, the Q output will be HIGH, and Q' will be LOW.
• When the D input is LOW and the clock pulse occurs, the Q output will be LOW, and Q' will be HIGH.

Applications of the 74LS74

D flip-flops are widely used in digital circuits for data storage, synchronization, and transfer. Common applications include:

• Data storage registers
• Shift registers
• Frequency dividers
• Edge detection circuits

Conclusion

In this experiment, we demonstrated how the 74LS74 D Flip-Flop can be used as a 1-bit data storage element. The flip-flop stores the value present on the D input when the clock signal transitions from low to high. It’s an essential building block in memory devices and sequential circuits.